The present invention pertains generally to voltage magnitude control systems and more specifically to feedback systems with signal level or other control means.
Prior systems have been able to control or regulate to some desired level the normally fluctuating input signal received by a radar or radio receiver either by limiting or by automatic gain control (AGC) in the IF amplifier but not by the combination of the two. An AGC system includes a feedback control loop which has a time constant depending upon the design of the loop. This gives a finite reaction time and thus it cannot respond instantaneously to a change in input signal level. Additionally, AGC systems have been shown to be influenced in an undesirable manner by interfering signals.
Limiting systems, on the other hand, respond to input level changes instantaneously and are not influenced by interfering signals in the same manner as AGC. The limiter, however, has another characteristic that can be a disadvantage in some applications. In the case of a short term signal dropout or severe level reduction, the limiter instantaneously supplies full gain and allows other signals of lower level to be received. These undesirable signals may add noise or errors to correct data already received and in some cases may capture other receiver circuits so as to prevent reception of the desired signal when it returns to full level.